I knew from some long-forgotten health class or Internet reading that spinach, which we have in abundance in our freezer, has lots of iron. But I also remembered something about there being a difference, nutritionally, between raw and cooked spinach. Was this true or not? Since I spent all day Googling to find the answer, I thought I'd collect everything I found for anyone else who'd ever had the same question.
Note: I'm not a doctor, nutritionist, chemist, biologist, or any other kind of expert. The following is the best possible synthesis I could generate of several disparate Internet sources. I did my best to verify everything but no one's ever perfect.
Why Do We Need Iron, Anyway?
Animals and plants both need iron. It's essential for respiration for both groups, though obviously plants and animals have very different respiratory needs. That's why the dietary iron in meat is different from the dietary iron in plant sources, but more on that later.
Oxygen transport is the arguably the foundation for health and fitness in humans; the more oxygen you can get to your muscles, the better you perform. The Lance Armstrong blood-doping scandal involved blood that had elevated levels of red blood cells—the cells that carry oxygen from the lungs to the muscles, using iron-containing hemoglobin. The doping thus increased the oxygen Armstrong and his teammates were able to supply to their muscles, boosting their endurance and aerobic capacity. In addition to transporting oxygen, iron is also important for the storage of oxygen in muscles and a few other sundry but important tasks.
Too much iron, however, is toxic. Fortunately for most grown humans, the body naturally reduces its absorption of iron if we take in too much. Most cases of iron toxicity occur in small children who think iron supplement pills look like candy—then it's too much, too quickly in a too-small body. There are also some genetic conditions that can lead to iron overload in adults.
How Do We Absorb Iron?
There are two kinds of iron, as far as nutrition is concerned: heme and nonheme. Heme iron is Fe+2 (yes, the same iron ion that contributes to aquamarine's coloring) surrounded by a ring consisting of carbon, hydrogen, and scant bits of oxygen and nitrogen. This is the form most often found in meat and is the kind our bodies absorb best, because animals use iron for the same reasons we do.
Dark, leafy green plants (and anything fortified with iron) contain nonheme iron, which as far as I can tell in my cursory research, is a kind of iron salt: FeCl2, 2 FeCl3, and so on. This makes sense; plants produce oxygen as a waste product, after all, so they don't need to really transport it to cells. Especially to the muscles they don't have. Even so, plant iron is still absorbed by humans—just not as efficiently (something like 10% to 20% from most plant sources, versus the 25% to 35% from animal sources). That's why doctors recommend that vegetarians and vegans consume more iron than meat-eaters. Your body doesn't absorb ALL of the iron (or other nutrients) that you consume.
A lot of the iron in your body is also stored (one could say "hoarded") for future use, mostly in the liver, spleen, and bone marrow. Red blood cells are also broken down and the body scavenges for any leftover iron, like scrap metal from a junked car. But entropy reigns supreme, and adults lose about 1 mg of iron every day. More if you're a woman, then it rises to about 1.5 to 2 mg (as a result of blood loss during menstruation). This is the point where I decided iron probably wasn't the key to my general malaise—thanks to the magic of hormonal birth control, my uterine lining stays right where it belongs and I don't otherwise bleed regularly. Nonetheless, what I found was still interesting, so I pressed on with my research.
When it comes to absorbing iron (and many other nutrients), our bodies tend to need a spoonful of sugar to help the medicine go down, as it were—other vitamins or nutrients to work in concert with the desired nutrient to facilitate its absorption. Iron is better-absorbed with vitamin C, for example.
Raw or Cooked?
The meat of the issue—or the vegetable protein of the issue, at any rate. Heating spinach does reduce some of its other nutrients by inducing certain chemical changes. This includes folate, niacin, potassium, riboflavin, and, with regards to iron absorption, vitamin C. However, cooked spinach contains greater absorbable amounts of vitamins A and E, fiber, zinc, thiamin, protein, and iron. It's not so much that heat creates nutrients ex nihilo; rather that it breaks down a given nutrient's inhibitors.
This is another compound found in spinach, and it dehydrates when heated. It has been demonstrated, in some studies, to inhibit iron absorption, leading some sources to question spinach's reputation as an iron powerhouse. Other studies have suggested, however, that oxalic's effect in iron absorption is negligible. So maybe you don't need to cook your spinach for iron after all?
How do you like your spinach? Raw or cooked?